The insulation cladding of pasta dryers has to meet various requirements. For one thing, any appreciable dissipation of energy through the cladding to the outside is to be prevented. A good insulation effect of cladding also has the consequence that there are correspondingly large temperature differences between the innermost and outermost skins of the cladding, which results in different thermal expansions on the cladding. To prevent air gaps developing between the wall elements, it is known to cover their joints with sealing tapes. However, this practice may, under extreme conditions, result in it only being possible to reseal the wall elements with the use of additional sealing material when fixed during service work following a lengthy time in operation. If, as is often the case today, flat boards are used here for wall elements, the problem indicated becomes even more difficult because the dimensional stability of these boards is less.
To achieve a better dimensional stability of the wall elements, wall elements having a slight convexity (large radius) in their middle region and provided with a greater curvature (smaller radius) at their edge regions (upper and lower end regions) have already been used, whereby an improved dimensional stability could be achieved. However, with these wall elements there is the risk that, not least also on account of the different curvature of the wall elements, uneven distributions of stresses may occur over the overall cross-section of the wall elements when there are substantial differences in temperature, leading to the risk of cracks forming.
In this situation, the invention is based on the object of fitting a pasta dryer with such insulation cladding that it results in an equalization of the stress distribution over the overall cross-section of the wall elements even when large temperature differences occur between inside and outside of the dryer, and thus in a reduced risk of cracks occurring. However, it is also the particular intention that quick removal and reattachment of the wall elements as often as desired for carrying out service work should be possible without any problems.
According to the invention, this object is achieved in the case of a pasta dryer of the type stated at the start by the wall elements being of convex design in the shape of a cylinder section and the associated frame parts being adapted accordingly.
It has been shown surprisingly that the measures according to the invention result in a surprisingly dimensionally stable behavior of the wall elements even with extreme temperature changes and large temperature differences and that, obviously owing to a noticeable equalization of the stress distribution over the area of the wall elements, it has been possible to reduce distinctly the risk of the undesired formation of cracks. Compared with the previously known wall elements, which were provided with an increased curvature in their edge regions, with the pasta dryer according to the invention there was also always a very effective sealing contact between the wall elements and the associated frame parts even if substantial temperature differences occurred. Thus, in the case of the invention, the use of additional sealing tapes can be dispensed with entirely, which is virtually impossible in the case of known dryers and also means that there may no longer be the necessity of renewing the seals after carrying out service work. It has proven advantageous to provide the wall elements with a uniform wall thickness over their entire area.
In the case of the invention, the wall elements are preferably lined on their side facing the inside of the dryer with a plate, again preferably made of thin metal sheet, loosely inserted into the bow shape as a vapor barrier. Depending on the type of operation, for example a 0.5 to 1 mm thick plate of, for example, stainless sheet steel may be inserted in this case without any rigid fixing on the inside of the particular wall element. Such a sheet steel plate proves in practice to be an effective vapor barrier, at the same time adapting without difficulty and completely of its own accord to the curvature of the wall element when inserted, as it has an appropriate flexibility over its entire area. This has the advantage that there is no need for any special working of the vapor barrier since, as already mentioned, the metal sheet easily adapts to the convex shape of the inside of the wall element (it should be borne in mind in this connection that these wall elements have a lengh and radius of curvature of an order of magnitude of 1 to 3 m). In this respect, care has to be taken merely that a suitable retaining fixture for such a plate as a vapor barrier is provided on the inside of the wall element, although this does not concern a retaining fixture by means of which the steel sheet is rigidly fixed to the wall element. Rather, such a retaining fixture is to be provided in which the sheet steel plate is only inserted and in which it can still expand or contract when temperature differences occur: the retaining fixture merely has to ensure that the inserted steel plate is adequately retained with respect to the wall element, for instance at its outer periphery, so that it cannot fall away from the wall element again. In the case of the invention, this can be performed for example in a particularly advantageous way by such a wall element being provided on its entire outer periphery on its inside (i.e. the side of the wall element facing the inside of the dryer) with a profiled seal, for instance a rubber profile, which is arranged in such a way that the plate-shaped vapor barrier is supported with respect to the wall element. In this case, it is also advantageous if the plate-shaped vapor barrier does not protrude laterally beyond such a profiled seal, for instance a rubber seal, (i.e. so that the rubber seal is arranged around the edge region of the wall element in such a way that the plate-shaped vapor barrier surrounded by the seal in its bordering edge region does not protrude by its lateral edges beyond the area enclosed by the seal). As the vapor barrier is only inserted into the retaining fixture, but is not to be connected to it rigidly with respect to the wall element, as consequently there is no fixed (rigid) connection between vapor barrier and wall element, the vapor barrier can also expand or contract independently of the wall element under the influence of temperature without undesired compulsive stresses occurring and yet is always retained adequately well by the profiled seal with respect to the wall element. The occurrence of undesired compulsive stresses may be avoided virtually completely in this case, which represents a quite substantial advantage over known constructions.
A further advantageous development of the invention consists in that the wall elements consist of foamed plastic or another insulating material which has a resistant outer skin, the outer skin of the wall element facing the inside of the dryer being provided with one or more grooves. The grooves, for instance in the form of depressions two to six fingers deep arranged distributed over the surface, produce not only a further dimensional reinforcement of the wall element concerned, but also make possible at the same time a reduction in the linear changes of the outer dimensions occurring on the inside of the wall (for instance due to higher temperatures), whereby it may be achieved that virtually no undesired thermal stresses occur any longer. As these grooves are completely covered by the vapor barrier (metal sheet), they do not produce any dirt traps either, which also permits quick and thorough cleaning of such a dryer.
A further advantageous development of the invention also consists in that each wall element is suspended at its upper side on hinges and can be pressed by means of tension elements arranged on its lower side against the corresponding frame parts, it being particularly advantageous if hinges are arranged in each case directly (vertically) above the tension elements. This makes possible further expedient practical handling when carrying out service work. At the same time, it is achieved that the respective convex wall element already bears well against the corresponding frame parts of the pasta dryer under its own weight, without the application of any additional force. By means of the tension elements, a completely tight finish around the entire periphery of the vapor barrier (wall element) can be ensured with only slight deformation of the sealing profile, and hence even when slight production inaccuracies occur.
Preferably, each wall element is assigned a support arm which is fixed on the frame part and can be folded down. If cleaning or other service work is to be carried out, two or three quick-acting closures can be opened quickly with few manipulations, the wall element pulled away at the bottom with one hand and the support arm, which holds it in an open position, moved into the desired position with the other hand. This makes it possible to reduce idle times noticeably compared with known solutions.
It is, furthermore, advantageous if the wall elements are designed with the same wall thickness over their entire area. As a vapor barrier can be inserted on the inside, the qualitative design of the wall elements and also the thickness of the insulating material of the wall elements can be chosen appropriately to meet other requirements, independently of the vapor barrier.